The invention relates to assays and more particularly to capturing and reporting the presence of a target, such as a pathogen.
Interest in Francisella tularensis has increased recently because of its potential use as an agent of biological warfare. Francisella tularensis is an intracellular, nonmotile, nonsporulating, Gram-negative bacterial pathogen that causes tularemia in man and animals. Its extreme hardiness, infectivity and the ability to cause lethal disease by aerosol raise serious concern that this organism can be exploited by terrorists as a possible biological weapon. As a result, tularemia bacteria is one of the high ranking pathogens categorized by CDC as a category A agent with the greatest impact on public health if it is used as a weapon of mass destruction. Human tularemia manifests itself in a variety of syndromes, most of them depending on the portal of infection. The clinical appearance varies from skin lesions to multiorgan involvement. Furthermore, the severity depends on the dose and the virulence of the pathogen. Francisella tularensis subsp. holarctica (type B) which is spread over the northern hemisphere is less virulent than Francisella tularensis sub tularensis (type A) which is distributed mainly in North America and is associated with a severe and generally fatal form of tularemia. In particular, typhoid and pneumonic forms are the most deadly with mortality that can exceed 30% if patients are left untreated. The current diagnostic test for tularemia is a colorimetric immunoagglutination assay based on a type B tularemia target. This type is immunologically indistinguishable from type A, the more pathogenic type. The military is more concerned with type A because of its potential as a very potent biological warfare or bioterrorism agent. Currently, PCR can distinguish type A from type B, but only by a difference in size of a specific PCR product. Also, the “gold standard” for distinguishing the two is culture. Type A can ferment glycerol, but type B cannot. Because of the high infectivity of small quantities of the bacteria, culture is not usually done, except in BSL3 laboratories.
Thus, there is a need for sensitive diagnostic systems and highly durable, reliable field tests, especially concerning pathogens that are potential agents of biological warfare (for example, an assay to replace the current immunoagglutination and antibody-based ELISA assays for the diagnosis of tularemia).